1. Field of the Invention
The present invention relates generally to materials that are used to store gas molecules, and specifically to materials that store molecular hydrogen by adsorption or absorption.
2. Background Art
Metal-organic frameworks (“MOFs”) are a rapidly growing class of porous materials for their amenability to design and extraordinary porosity. The recent discovery that MOFs take up significant amounts of hydrogen has further intensified research in this area. In particular, the focus remains on identifying strategies for designing MOF structures that would be capable of high hydrogen storage capacity. Metal-oxide units and the organic linkers have been identified as important features for hydrogen binding. More recently, it has been shown that interpenetrating MOFs take up more hydrogen than their non-interpenetrating analogues.
The synthetic conditions that produce Cu2(CO2)4 “paddlewheel” units in metal-organic frameworks (“MOFs”), and the use of these materials in the design of 0-periodic discrete and 3-periodic extended structures are known. MOF-505 is synthesized using analogous conditions: the solvothermal reaction of 3, 3′, 5, 5′-biphenyltetracarboxylic acid (“H4BPTC”) (25 mg, 0.076 mmol) and Cu(NO3)2.(H2O)2.5 (52 mg, 0.22 mmol) in N,N-dimethylformamide (DMF)/ethanol/H2O (3:3:2 ml) at 65° C. for 24 hrs gave green block shaped crystals (47 mg, 86% yield based on H4BPTC). The resulting compound was found to be consistent with a formula of Cu2(BPTC)(H2O)2.(DMF)3(H2O) by elemental microanalysis and single-crystal X-ray diffraction studies.
Currently, there is much interest in developing methodology and systems for storing hydrogen for a variety of applications. For example, hydrogen is an important fuel for fuel cells which generate electricity by the electrochemical oxidation of hydrogen. Moreover, hydrogen as a combustion fuel is very environmentally friendly, generating only water as a combustion byproduct. Hydrogen storage for such applications is complicated by the fact that molecular hydrogen gas is flammable and in some situations explosive. Alternative methodology for storing hydrogen exist, but each of the current alternatives are undesirable for one or more reasons.
Carbon dioxide removal is another current area of significant interest. Removal of carbon dioxide from the flue exhaust of power plants, currently a major source of anthropogenic carbon dioxide, is commonly accomplished by chilling and pressurizing the exhaust or by passing the fumes through a fluidized bed of aqueous amine solution, both of which are costly and inefficient. Other methods based on chemisorption of carbon dioxide on oxide surfaces or adsorption within porous silicates, carbon, and membranes have been pursued as means for carbon dioxide uptake. However, in order for an effective adsorption medium to have long term viability in carbon dioxide removal it should combine two features: (i) a periodic structure for which carbon dioxide uptake and release is fully reversible, and (ii) a flexibility with which chemical functionalization and molecular level fine-tuning can be achieved for optimized uptake capacities.
Accordingly, there is a need for material with high molecular hydrogen storage capacity.